In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed for use by the military. In this type of network, each mobile node is capable of operating as a base station or router for other mobile nodes, thereby eliminating the need for a fixed infrastructure of base stations. The communications signals include, for example, voice data that has been modulated according to a desired modulation technique and transmitted as data packets. As can be appreciated by one skilled in the art, network nodes transmit and receive data packet communications in a multiplexed format, such as time-division multiple access (TDMA) format, code-division multiple access (CDMA) format, or frequency-division multiple access (FDMA) format, which enables a single transceiver at the base node to communicate simultaneously with several mobile nodes in its coverage area.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in a conventional ad-hoc network, further enable the mobile nodes to access a fixed network and communicate with other mobile nodes, such as those on the public switched telephone network (PSTN), and on other networks, such as the Internet. Details of these advanced types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29,2001, now U.S. Pat. No. 7,072,650, granted on Jul. 04, 2006, in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, now U.S. Pat. No. 6,807,165, and in U.S. patent application Ser. No. 09/815,164 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, filed on Mar. 22, 2001, now U.S. Pat. No. 6,873,839, the entire content of each being incorporated herein by reference.
As can be appreciated by one skilled in the art, communication between nodes, however, is often subject to errors due to interference, multipath and fading effects, and collisions. Avoidance of many such errors can be achieved using a control-signal handshake between transmitting and receiving nodes. A communication protocol, such as multiple access with collision avoidance (MACA), uses such a handshake technique between nodes consisting of a request-to-send (RTS) control packet sent from a source node to a destination node which in response, replies with a clear-to-send (CTS) control packet. A multiple access with collision avoidance for wireless (MACAW) algorithm typically handles ARQ retransmissions for corrections of such errors by repeating the whole request-to-send/clear-to-send (RTS/CTS) channel access sequence. In addition, MACAW introduces the use of data-sending (DS) messages to form RTS-CTS-DS-DATA-ACK message exchange and a new backoff algorithm (with the “DATA” being the data and “ACK” being and acknowledgement message).
The Institute of Electrical and Electronics Engineers (IEEE) 802.11 Standard has a mandatory access method, referred to as a distributed coordination function (DCF), which is a form of carrier sense multiple access with collision avoidance (CSMA/CA) that implements both carrier sensing and virtual (RTS-CTS exchange) carrier sensing with acknowledgment messages to improve reliability. As an optional access method, the IEEE 802.11 Standard defines a method known as a point coordination function (PCF), which enables the transmission of time-sensitive information. With PCF, a point coordinator within the access point (AP) controls which stations can transmit during any given period of time. Within a time period called the contention free period, the point coordinator steps through a list of the stations operating in PCF mode and polls them one at a time.
In addition, the media access control (MAC) according to the IEEE 802.11e Standard provides QoS enhancements. That is, the 802.11e Standard QoS technique employs a coordination function called hybrid coordination function (HCF) used only in a QoS enhanced basic service set (QBSS). The HCF has two modes of operation: enhanced distributed channel access (EDCA) and HCF controlled channel access (HCCA). As can be appreciated by one skilled in the art, EDCA is a contention-based channel access function that operates concurrently with HCCA based on a polling mechanism, which is controlled by the hybrid coordinator (HC). The HC is co-located with the QAP (QoS AP), and both types of access (EDCA and HCCA) enhance or extend functionality of the original access methods DCF and PCF. EDCA has been designed for support of prioritized traffic similar to DiffServ (Differentiated Services), which is a protocol for specifying and controlling network traffic by class so that certain types of traffic get precedence, whereas HCCA supports parameterized traffic similar to IntServ (Integrated Services), which is a protocol that attempts to guarantee QoS on networks.
The IEEE 802.11 Standard further introduces the concept of transmission opportunity (TXOP) that is a bounded time interval in which the QSTA (QoS station) is allowed to transmit a series of frames. A TXOP is defined by the start time and a maximum duration. If a TXOP is obtained using the contention-based channel access, it is called an EDCA-TXOP. If a TXOP is granted through HCCA, it is called a HCCA (polled) TXOP. Furthermore, the IEEE 802.11e Standard defines different acknowledgement (ACK) policies between nodes.
Other MAC protocols, such as TDMA based systems, have been proposed for ad-hoc wireless systems to support guaranteed QoS provision. Due to lack of a central controller and high network dynamics, end-to-end reservation schemes or admission control schemes, however, are often not feasible to implement. On the other hand, hop-by-hop channel reservation and traffic control systems may fail to work efficiently if appropriate actions are not taken along the path of the traffic flow. The problem gets more complicated when there are multiple options for MAC protocols along a path since the devices may have multiple transceivers.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.